Electromagnetic radiation is a common concern today due to the believed deleterious effects caused by varying degrees of exposure. This type of radiation is defined as waves of energy, consisting of electric and magnetic fields, vibrating at right angles to the direction of wave propagation. Electromagnetic waves are divided into six basic categories dependent on wavelength. In order of wavelength, longest to shortest, electromagnetic waves are categorized as: (i) radio waves, having a wavelength of 10.sup.5 -10.sup.-3 meters; (ii) infrared (heat) waves, having a wavelength of 10.sup.-3 -10.sup.-6 meters; (iii) visible light, having a wavelength of 10.sup.-6 -10.sup.-7 meters; (iv) ultraviolet waves, having a wavelength of 10.sup.-7 -10.sup.-9 meters; (v) x-rays, having a wavelength of 10.sup.-9 -10.sup.-11 meters; and (vi) gamma rays, having a wavelength of 10.sup.-11 -10.sup.-14 meters. The most common type of radiation causing concern to humans is in the form of ultraviolet radiation. Ultraviolet rays are known to be produced by the sun and various industrial sources such as arc welding, tanning equipment, ultraviolet lasers and lithography exposure equipment, as well as other various means. Ultraviolet rays are typically categorized according to wavelength and known as UV-A rays, UV-B rays and UV-C rays. UV-A rays range from 315-400 nanometers and are responsible for tanning in humans, skin cancer, eye cataracts, solar retinitis and corneal dystrophies. UV-A rays can also cause erythema, but levels 800-1000 times higher than those of UV-B rays are required. In addition, UV-A rays are known to penetrate deeper than UV-B rays. UV-B rays range from 285-318 nanometers in wavelength and are generally considered to be the greatest cause of skin cancer in humans. UV-B rays are the cause of erythema, sunburn and the greatest factor in much of the dermal-connective tissue destruction found in the photoaging process. UV-C rays range from 200-285 nanometers in wavelength and usually are absorbed prior to reaching earth in the upper atmosphere. In general, human exposure to ultraviolet radiation is characterized by vasodilation and an increase in the volume of blood in the dermis. This increased volume of blood is perceived as a reddening of the skin. Knowledge of the cumulative exposure to ultraviolet radiation would greatly assist in allowing one to avoid the harmful effects of ultraviolet radiation.
Short wavelength electromagnetic radiation of other types is typically found in the form of gamma rays and x-rays. X-rays are a form of electromagnetic radiation, falling between ultraviolet radiation and gamma rays in the electromagnetic spectrum. X-ray radiation is produced by bombarding a solid target with a beam of high energy electrons. X-rays can pass through many forms of matter, and therefore are typically found in medical and industrial practice applications to examine internal structures. Falling at the end of the electromagnetic spectrum, gamma rays are still shorter in wavelength. Gamma rays are a form of radiation emitted during the course of nuclear reactions when an excited atomic nuclei passes to a lower excitation state. Typically, gamma rays are produced in radioactive decay processes. Similar to ultraviolet radiation, both gamma rays and x-rays are responsible for creating many injurious effects to humans upon repetitive exposure.
The measurement of exposure to ultraviolet radiation and other forms of radiation in everyday activities and industrial type work is crucial for the determination of total dosage of exposure which is believed to promote skin cancer and other deleterious effects to the individual. It has been determined that frequent and prolonged exposure to ultraviolet radiation and other forms of radiation over many years will induce cellular changes in the human skin. The knowledge of the total exposure dosage, not the rate of exposure dosage, is most beneficial to the individual.
There are at the present many products on the market which offer exposure protection against believed harmful radiation, generally for protecting against ultraviolet radiation. The most common and commercially available product is in the form of sunscreens, offering various sun protection factors for varying types of skin. The most common sunscreens are in the form of lotions, cremes and oils which are intended to be applied directly to the skin prior to ultraviolet exposure. The incorporation of skin protectants upon exposure is a necessity for simulating actual skin condition and determining an accurate cumulative ultraviolet exposure value.
The photo-induced effect of chalcogenide glasses is considered to be of great technological importance in the pursuit of measuring radiation exposure. Changes which range from a subtle shift in the arrangement of atoms to more substantial physical and chemical rearrangements, have been documented upon exposure to light or radiation. Well known in today's technical works are seven distinguishable photo-induced structural or physico-chemical changes occurring in chalcogenides. Included in these physical and chemical changes are: (i) photo-crystallization, the formation of crystals from an amorphous state upon exposure to light or irradiation; (ii) photo-enhanced dissolution of metals, the dissolving of a thin metallic layer into and through an amorphous film upon exposure to light or irradiation; (iii) photo-polymerization, the process in which light sensitive polymers undergo a spontaneous and permanent change in physical properties upon exposure to light or irradiation; (iv) photo-decomposition, the breakdown of a composition into its constituent parts; (v) photo-induced morphological changes, the change in form and structure which takes place upon exposure to light or irradiation; (vi) photo-vaporization, the photo-oxidation reaction subsequent to thermal evaporation; and (vii) photo-induced changes in atomic structure, the changes induced by light emitted by photon energy. (Owen, A. E., et al., Philosophical Magazine B, 1985, 52:3, 347-362.) These changes are classified based on whether they are reversible or irreversible and whether they are basically structural or physico-chemical in type.
There exist today many instruments for measuring exposure to ultraviolet radiation. Many of these instruments are commercially available as patches or devices capable of attachment to clothing. These instruments measure exposure to ultraviolet radiation through the use of gas chromatography, thermoluminescent radiation, substrate layering, oscillation energy and electrical resistance.
U.S. Pat. No. 4,763,011, issued to Smith, illustrates the use of gas chromatography to determine ultraviolet exposure. The Smith patent discloses an ultraviolet radiation actinometer or dosimeter capable of measuring the change in concentration of a reaction product through gas chromatography. The patent teaches an apparatus that depends upon a reaction between a solubilized alkyl disulfide and ultraviolet radiation. The alkyl disulfide is dissolved in a solvent and donates hydrogen atoms upon exposure to ultraviolet radiation to form a stable thiol or disulfide which is then detectable by gas chromatography. The process involves the use of the actinometer or dosimeter, but fails to disclose the process of photodissolution, incorporating the use of a chalcogenide glass, nor the alteration and measurement of an electrical resistance.
U.S. Pat. No. 5,008,548, issued to Gat, discloses a miniature portable battery operated power/energy radiometer appropriate for personal use. It provides both for the measurement of the total energy overtime or overall dosage and for the determination of the direction of maximum radiant ultraviolet power. The instrument contains a radiation sensor, a power meter means for displaying radiation intensity and a dosage meter means for displaying radiation dosage. The controller for the instrument is a microprocessor which processes electrical signals from a photocell using an integrated circuit chip.
Additionally, instruments which utilize the chemical reaction of photo-sensitive materials in a layered form are recognized in the current patent literature. U.S. Pat. No. 4,825,084, issued to Braunlich, et al., discloses a thin layer thermoluminescent radiation dosimeter for use in laser readable dosimetry systems and a method for using said dosimeter. The dosimeter as taught is made of a substrate comprised of a transparent glass or a nonporous ceramic, a phosphor-matrix layer bonded to the substrate with an interconnecting binder, a reflective material coating and a moisture resistant protective envelope. Upon exposure, the electrons contained within the thermoluminescent dosimeter become highly energized and trapped at a higher energy level until allowed to fall back to a lower energy state through additional energy, in the form of heat. This addition of energy releases the trapped electrons in the form of visible light which is termed a luminescent emission. This luminescent emission is the measured product used to determine the dosage of radiation exposure.
U.S. Pat. No. 5,083,031, issued to Hoelsher et al. is a continuation-in-part of the Braunlich patent previously discussed. The Hoelsher patent discloses the use of thin layer substrates. In addition, the patent teaches the use of a memory chip to store calibration and identification information which is used during the reading of the device. Once again, the exposure dosage is determined by the luminescent emission which is read by a stimulating laser beam.
The current patent literature includes various types of personal actinometers and dosimeters. These instruments determine exposure to ultraviolet radiation. Currently, none of these instruments allow for total cumulative exposure to ultraviolet light or irradiation over an extended period of time. The currently available instruments retain data, dependent upon a continuous power supply; however, once the power supply to the device is turned off, the cumulative data is lost. Lacking in the patent literature is a personal electronic ultraviolet dosimeter as described in the present invention which is capable of measuring cumulative ultraviolet radiation exposure, or exposure to radiation of shorter wavelengths, through the irreversible process of the dissolution of a metal into a chalcogenide glass. There exist in the present invention no loss of cumulative data due to its lack of dependence on a constant power source. The dissolution of the metal in the metal-containing film into the chalcogenide results in a decrease in the thickness of the exposed metal-containing film, thereby increasing the electrical resistance of the exposed metal-containing film. This increase in electrical resistance of the metal-containing film is capable of being measured and converted into a cumulative exposure dosage value based on approved dermatologist recommended exposure levels.
There is a need for an instrument capable of recording the actual cumulative exposure to radiation, which can be worn directly on the skin or on or under clothing. The user of the personal electronic dosimeter, when measuring ultraviolet radiation, is able to directly apply an exposure protectant to the portion of the dosimeter which receives and interprets the illumination of ultraviolet rays. Sunblock or protective coatings may be applied directly to the device to simulate actual skin exposure thus enabling the individual to obtain the best assessment of exposure to the radiation. This direct application enables the dosimeter to measure and interpret an accurate cumulative ultraviolet radiation exposure dosage value.
The current invention relates to a device which measures exposure to radiation in the form of ultraviolet radiation or other forms of short wavelength electromagnetic radiation. Exposure dosage is determined through the photodissolution of a metal-containing film into a chalcogenide glass upon illumination or exposure. Photodissolution is defined as the process that takes place upon exposure to light or irradiation of the correct wavelength, thus causing a metal from a metal-containing film to become dissolved into a chalcogenide glass. Specific metals and chalcogenides may be used dependent on the specific radiation wavelength of which exposure is sought to be measured and to reduce the effects of thermal diffusion upon exposure. During photodissolution, exposure to radiation causes the metal of the metal-containing film to rapidly dissolve into the chalcogenide and migrate through the chalcogenide. Exposure in the form of vertical illumination will cause the metal in the metal-containing film to migrate vertically with minimal lateral movement. The radiation exposure which takes place causes an increase in the electrical resistance of the exposed metal-containing film by thinning the film layer. The electrical resistance of the metal-containing film is subsequently measured to determine the change in electrical resistance which occurred between the exposed portion and the shielded, unexposed, portion of the metal-containing film. The actual exposure to ultraviolet light or irradiation is determined by the change in electrical resistance. The dissolution effect which takes place is irreversible thus, the cumulative dosage information cannot be lost. The means for measuring the change in electrical resistance can be a simple differential amplifier integrated circuit which measures the difference in electrical resistance between the light and dark effects of the metal-containing film. The light and dark effects are created by exposing one portion of the metal-containing film to some form of radiation while shielding another portion of the metal-containing film from radiation exposure. This difference in electrical resistance is subsequently converted into a cumulative exposure dosage value and sent to an appropriate output device.
The actual form of the dosimeter may be a small patch or button, powered by a low cost battery or solar cell.